Open loop spatial processing

ABSTRACT

Methods and apparatus for multiple-input multiple-output (MIMO) transmissions are disclosed. A base station may precode wireless transmit/receive unit (WTRU)-specific reference signals and data that are transmitted to a WTRU using a randomly selected precoder. The precoder may be selected based on a predefined precoder selection sequence or by the base station. A different precoder may be applied to different resource blocks (RBs). In addition, a large delay cyclic delay diversity (CDD) or discrete Fourier transform (DFT) spreading may be applied on the WTRU-specific reference signals and the data. For heterogeneous deployed antennas, spatial diversity gain is achieved by dynamically scheduling resources between transmission points. A hopping scheme may be applied across the transmission points as the resources are dynamically partitioned between the transmission points. A different randomly selected precoder may be applied to each RB transmitted from a different transmission point.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/457,145, filed Apr. 26, 2012, which claims the benefit of U.S.provisional application No. 61/480,459, filed Apr. 29, 2011, thecontents of which are hereby incorporated by reference herein.

FIELD OF THE INVENTION

This application is related to wireless communications.

BACKGROUND

Both open-loop and closed-loop multiple-input multiple-output (MIMO)schemes in the form of spatial multiplexing (SM) have been introduced in3rd Generation Partnership Project (3GPP) long term evolution (LTE)Release 8 (R8) for downlink transmissions. Closed-loop spatialmultiplexing refers to linearly precoded MIMO transmissions where eitherfull or partial channel state information (CSI) is available at thetransmitter. Open-loop spatial multiplexing corresponds to MIMOtransmissions where CSI is not available at the transmitter or ispartially available, (e.g., long-term measurements may be available butshort-term measurements allowing fast adaptation are not). Open-loopspatial multiplexing is a good candidate for high mobility cases.

SUMMARY

Methods and apparatus for multiple-input multiple-output (MIMO)transmissions are disclosed. A base station may precode wirelesstransmit/receive unit (WTRU)-specific reference signals and data thatare transmitted to a WTRU using a randomly selected precoder. Theprecoder may be selected based on a predefined precoder selectionsequence or by the base station. A different precoder may be applied todifferent resource blocks (RBs). In addition, a large delay cyclic delaydiversity (CDD) or discrete Fourier transform (DFT) spreading may beapplied on the WTRU-specific reference signals and the data. Forheterogeneous deployed antennas, spatial diversity gain is achieved bydynamically scheduling resources between transmission points. A hoppingscheme may be applied across the transmission points as the resourcesare dynamically partitioned between the transmission points. A differentrandomly selected precoder may be applied to each RB transmitted from adifferent transmission point.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1A is a system diagram of an example communications system in whichone or more disclosed embodiments may be implemented;

FIG. 1B is a system diagram of an example wireless transmit/receive unit(WTRU) that may be used within the communications system illustrated inFIG. 1A;

FIG. 1C is a system diagram of an example radio access network and anexample core network that may be used within the communications systemillustrated in FIG. 1A;

FIG. 2 illustrates a transmit chain of open-loop spatial multiplexing inlong term evolution release 8;

FIG. 3 shows an example random precoding block diagram; and

FIG. 4 shows an example open-loop spatial multiplexing fromgeographically distributed transmit antennas.

DETAILED DESCRIPTION

FIG. 1A is a diagram of an example communications system 100 in whichone or more disclosed embodiments may be implemented. The communicationssystem 100 may be a multiple access system that provides content, suchas voice, data, video, messaging, broadcast, etc., to multiple wirelessusers. The communications system 100 may enable multiple wireless usersto access such content through the sharing of system resources,including wireless bandwidth. For example, the communications systems100 may employ one or more channel access methods, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrierFDMA (SC-FDMA), and the like.

As shown in FIG. 1A, the communications system 100 may include wirelesstransmit/receive units (WTRUs) 102 a, 102 b, 102 c, 102 d, a radioaccess network (RAN) 104, a core network 106, a public switchedtelephone network (PSTN) 108, the Internet 110, and other networks 112,though it will be appreciated that the disclosed embodiments contemplateany number of WTRUs, base stations, networks, and/or network elements.Each of the WTRUs 102 a, 102 b, 102 c, 102 d may be any type of deviceconfigured to operate and/or communicate in a wireless environment. Byway of example, the WTRUs 102 a, 102 b, 102 c, 102 d may be configuredto transmit and/or receive wireless signals and may include userequipment (UE), a mobile station, a fixed or mobile subscriber unit, apager, a cellular telephone, a personal digital assistant (PDA), asmartphone, a laptop, a netbook, a personal computer, a wireless sensor,consumer electronics, and the like.

The communications systems 100 may also include a base station 114 a anda base station 114 b. Each of the base stations 114 a, 114 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to one or morecommunication networks, such as the core network 106, the Internet 110,and/or the networks 112. By way of example, the base stations 114 a, 114b may be a base transceiver station (BTS), a Node-B, an eNode-B, a HomeNode-B, a Home eNode-B, a site controller, an access point (AP), awireless router, and the like. While the base stations 114 a, 114 b areeach depicted as a single element, it will be appreciated that the basestations 114 a, 114 b may include any number of interconnected basestations and/or network elements.

The base station 114 a may be part of the RAN 104, which may alsoinclude other base stations and/or network elements (not shown), such asa base station controller (BSC), a radio network controller (RNC), relaynodes, etc. The base station 114 a and/or the base station 114 b may beconfigured to transmit and/or receive wireless signals within aparticular geographic region, which may be referred to as a cell (notshown). The cell may further be divided into cell sectors. For example,the cell associated with the base station 114 a may be divided intothree sectors. Thus, in one embodiment, the base station 114 a mayinclude three transceivers, i.e., one for each sector of the cell. Inanother embodiment, the base station 114 a may employ multiple-inputmultiple output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 116, which may beany suitable wireless communication link, (e.g., radio frequency (RF),microwave, infrared (IR), ultraviolet (UV), visible light, etc.). Theair interface 116 may be established using any suitable radio accesstechnology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 104 and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access (UTRA), whichmay establish the air interface 116 using wideband CDMA (WCDMA). WCDMAmay include communication protocols such as High-Speed Packet Access(HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed DownlinkPacket Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA).

In another embodiment, the base station 114 a and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Evolved UMTSTerrestrial Radio Access (E-UTRA), which may establish the air interface116 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.16 (i.e.,Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000,CDMA2000 1×, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), InterimStandard 95 (IS-95), Interim Standard 856 (IS-856), Global System forMobile communications (GSM), Enhanced Data rates for GSM Evolution(EDGE), GSM EDGE (GERAN), and the like.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. In oneembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayimplement a radio technology such as IEEE 802.11 to establish a wirelesslocal area network (WLAN). In another embodiment, the base station 114 band the WTRUs 102 c, 102 d may implement a radio technology such as IEEE802.15 to establish a wireless personal area network (WPAN). In yetanother embodiment, the base station 114 b and the WTRUs 102 c, 102 dmay utilize a cellular-based RAT, (e.g., WCDMA, CDMA2000, GSM, LTE,LTE-A, etc.), to establish a picocell or femtocell. As shown in FIG. 1A,the base station 114 b may have a direct connection to the Internet 110.Thus, the base station 114 b may not be required to access the Internet110 via the core network 106.

The RAN 104 may be in communication with the core network 106, which maybe any type of network configured to provide voice, data, applications,and/or voice over internet protocol (VoIP) services to one or more ofthe WTRUs 102 a, 102 b, 102 c, 102 d. For example, the core network 106may provide call control, billing services, mobile location-basedservices, pre-paid calling, Internet connectivity, video distribution,etc., and/or perform high-level security functions, such as userauthentication. Although not shown in FIG. 1A, it will be appreciatedthat the RAN 104 and/or the core network 106 may be in direct orindirect communication with other RANs that employ the same RAT as theRAN 104 or a different RAT. For example, in addition to being connectedto the RAN 104, which may be utilizing an E-UTRA radio technology, thecore network 106 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 106 may also serve as a gateway for the WTRUs 102 a,102 b, 102 c, 102 d to access the PSTN 108, the Internet 110, and/orother networks 112. The PSTN 108 may include circuit-switched telephonenetworks that provide plain old telephone service (POTS). The Internet110 may include a global system of interconnected computer networks anddevices that use common communication protocols, such as thetransmission control protocol (TCP), user datagram protocol (UDP) andthe internet protocol (IP) in the TCP/IP internet protocol suite. Thenetworks 112 may include wired or wireless communications networks ownedand/or operated by other service providers. For example, the networks112 may include another core network connected to one or more RANs,which may employ the same RAT as the RAN 104 or a different RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, i.e., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks. For example, the WTRU 102 c shown in FIG. 1A may be configured tocommunicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B is a system diagram of an example WTRU 102. As shown in FIG. 1B,the WTRU 102 may include a processor 118, a transceiver 120, atransmit/receive element 122, a speaker/microphone 124, a keypad 126, adisplay/touchpad 128, non-removable memory 130, removable memory 132, apower source 134, a global positioning system (GPS) chipset 136, andother peripherals 138. It will be appreciated that the WTRU 102 mayinclude any sub-combination of the foregoing elements while remainingconsistent with an embodiment.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, thetransmit/receive element 122 may be an antenna configured to transmitand/or receive RF signals. In another embodiment, the transmit/receiveelement 122 may be an emitter/detector configured to transmit and/orreceive IR, UV, or visible light signals, for example. In yet anotherembodiment, the transmit/receive element 122 may be configured totransmit and receive both RF and light signals. It will be appreciatedthat the transmit/receive element 122 may be configured to transmitand/or receive any combination of wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 1B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, in one embodiment, the WTRU 102 mayinclude two or more transmit/receive elements 122 (e.g., multipleantennas) for transmitting and receiving wireless signals over the airinterface 116.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 130 and/or the removable memory 132.The non-removable memory 130 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information, (e.g., longitude andlatitude), regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 116 from abase station, (e.g., base stations 114 a, 114 b), and/or determine itslocation based on the timing of the signals being received from two ormore nearby base stations. It will be appreciated that the WTRU 102 mayacquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

FIG. 1C is a system diagram of the RAN 104 and the core network 106according to an embodiment. As noted above, the RAN 104 may employ anE-UTRA radio technology to communicate with the WTRUs 102 a, 102 b, 102c over the air interface 116. The RAN 104 may also be in communicationwith the core network 106.

The RAN 104 may include eNode-Bs 140 a, 140 b, 140 c, though it will beappreciated that the RAN 104 may include any number of eNode-Bs whileremaining consistent with an embodiment. The eNode-Bs 140 a, 140 b, 140c may each include one or more transceivers for communicating with theWTRUs 102 a, 102 b, 102 c over the air interface 116. In one embodiment,the eNode-Bs 140 a, 140 b, 140 c may implement MIMO technology. Thus,the eNode-B 140 a, for example, may use multiple antennas to transmitwireless signals to, and receive wireless signals from, the WTRU 102 a.

Each of the eNode-Bs 140 a, 140 b, 140 c may be associated with aparticular cell (not shown) and may be configured to handle radioresource management decisions, handover decisions, scheduling of usersin the uplink and/or downlink, and the like. As shown in FIG. 1C, theeNode-Bs 140 a, 140 b, 140 c may communicate with one another over an X2interface.

The core network 106 shown in FIG. 1C may include a mobility managementgateway entity (MME) 142, a serving gateway 144, and a packet datanetwork (PDN) gateway 146. While each of the foregoing elements aredepicted as part of the core network 106, it will be appreciated thatany one of these elements may be owned and/or operated by an entityother than the core network operator.

The MME 142 may be connected to each of the eNode-Bs 140 a, 140 b, 140 cin the RAN 104 via an S1 interface and may serve as a control node. Forexample, the MME 142 may be responsible for authenticating users of theWTRUs 102 a, 102 b, 102 c, bearer activation/deactivation, selecting aparticular serving gateway during an initial attach of the WTRUs 102 a,102 b, 102 c, and the like. The MME 142 may also provide a control planefunction for switching between the RAN 104 and other RANs (not shown)that employ other radio technologies, such as GSM or WCDMA.

The serving gateway 144 may be connected to each of the eNode Bs 140 a,140 b, 140 c in the RAN 104 via the S1 interface. The serving gateway144 may generally route and forward user data packets to/from the WTRUs102 a, 102 b, 102 c. The serving gateway 144 may also perform otherfunctions, such as anchoring user planes during inter-eNode-B handovers,triggering paging when downlink data is available for the WTRUs 102 a,102 b, 102 c, managing and storing contexts of the WTRUs 102 a, 102 b,102 c, and the like.

The serving gateway 144 may also be connected to the PDN gateway 146,which may provide the WTRUs 102 a, 102 b, 102 c with access topacket-switched networks, such as the Internet 110, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and IP-enableddevices.

The core network 106 may facilitate communications with other networks.For example, the core network 106 may provide the WTRUs 102 a, 102 b,102 c with access to circuit-switched networks, such as the PSTN 108, tofacilitate communications between the WTRUs 102 a, 102 b, 102 c andtraditional land-line communications devices. For example, the corenetwork 106 may include, or may communicate with, an IP gateway (e.g.,an IP multimedia subsystem (IMS) server) that serves as an interfacebetween the core network 106 and the PSTN 108. In addition, the corenetwork 106 may provide the WTRUs 102 a, 102 b, 102 c with access to thenetworks 112, which may include other wired or wireless networks thatare owned and/or operated by other service providers.

FIG. 2 illustrates a transmit chain 200 of open-loop spatialmultiplexing in LTE Release 8 (LTE R8). Codewords are precoded throughthe use of a combination of three matrices, where the matrix U 205 inthe chain 200 is a fixed DFT precoder, the matrix D(i) 210 is a diagonalmatrix representing the large delay cyclic delay diversity (CDD)functionality, and the matrix W 215 is the precoder defined forclose-loop spatial multiplexing.

The closed-loop precoding scheme in LTE-Advanced (LTE-A), (referringalso to LTE Release 10 and beyond), is extended over the LTE R8 schemeto support configurations with up to 8 transmit antennas in the downlinkusing a WTRU-specific reference signal to improve data coverage.

In low speed conditions, the closed-loop spatial multiplexing (CL-SM)mode may significantly improve downlink data throughput by usingprecoding on the transmitted signal before the channel has changedsignificantly. For moderate and high speed conditions, due to estimationand transmission delays, it is difficult to provide reliable andaccurate channel state information (CSI) at the base station. In suchcases, the open-loop SM (OL-SM) schemes may perform better than theCL-SM schemes.

The OL-SM may be used to reduce the uplink feedback signaling overhead.For instance, in LTE Release 11 (LTE R11), multi-cell coordinatedmulti-point transmission (CoMP) may improve the overall cell throughputand efficiency. For efficient CoMP operations, the WTRU may feedback CSIfor multiple transmission points (TPs). This implies that the amount offeedback overhead in CoMP may significantly increase, particularly for alarge number of WTRUs.

In general, the benefit of OL-SM is reduced by antenna correlation. Thisproblem may be addressed to some extent by using cross polarizedantennas. However, as the technology evolves from more conventionaldeployment types to new heterogeneous deployments, such as those using ashared cell ID distributed antennas approach, an additionalde-correlation between the spatial streams at different transmissionpoints may be obtained. Techniques, such as OL-SM may be particularlybeneficial in some specific deployment scenarios, such as those using ashared cell identity (ID) distributed antenna scheme, regardless of theWTRU velocity.

With the introduction of WTRU-specific reference signals orWTRU-specific demodulation reference signals (DM-RS) for use in CL-SM inLTE R10, the downlink (DL) multi-user (MU)-MIMO performance may besignificantly improved. However, the open-loop MIMO operation in LTE R8was originally designed to offer a competitive performance as comparedto single-user (SU)-MIMO using cell-specific reference signals (CRS).Therefore, OL-SM schemes which demonstrate an improvement in MU-MIMOperformance over that of LTE R8 or LTE R10 are of importance.

Described herein are OL-SM methods using DM-RS for homogeneous andheterogeneous deployments. In an example method, data and referencesymbols are jointly precoded using a single precoder. In particular,DM-RS and data, (i.e., identified with a physical downlink sharedchannel (PDSCH)), that are transmitted to a WTRU may be precoded using arandomly selected precoder. The precoder may belong to a codebook whichcontains a set of precoders known to both the base station and the WTRU.Hereafter, the random precoder selection may refer to a predefinedprecoder selection sequence or a precoder determined by the base stationand not necessarily known to the WTRU. In the case where the WTRU doesnot know the exact precoder used by the base station for a giventransmission, it may be assumed that dedicated pilots may be transmittedby the base station and used by the WTRU for data demodulation. The termdedicated pilots may refer to CRS′ or DM-RS′. In an example, DM-RS′ aretransmitted by the base station and used by the WTRU for datademodulation.

As shown in FIG. 3, a PDSCH allocation 300 may comprise multipleresource blocks (RBs) . . . , n, n+1, n+2, n+3, . . . , and a randomlyselected precoder 305 may be different for different RBs . . . , n, n+1,n+2, n+3, . . . . In this example method, the DM-RSs 310 and associateddata channel(s) (i.e., the PDSCHs) 300 sweep different directions acrossmultiple RBs which may cause the channel to appear ergodic or differentat the WTRU(s). The term C_(n) refers to a specific occurrence of aprecoder codevector that is derived from W(i) as shown herein below.

The WTRU may be configured through either physical layer signaling,(via, for example, a physical data control channel (PDCCH)), or higherlayer signaling. The signaling may include precoding granularityinformation, i.e., information indicating the number of RBs applicableto a randomly selected precoder.

In case of per-RB precoding, the WTRU may perform channel estimation ona single RB. Alternatively, in order to improve channel estimationperformance at the WTRU, a randomly selected precoder may be appliedacross multiple RBs. In this case, the WTRU may perform channelestimation using multiple RBs using, for example, interpolation and/orextrapolation.

The precoded P×1 vector for OL-SM, (where P is the number of transmitantennas), may be defined as follows:

$\begin{matrix}{{\begin{bmatrix}{y^{(0)}(i)} \\\vdots \\{y^{({P - 1})}(i)}\end{bmatrix} = {{W(i)}\begin{bmatrix}{x^{(0)}(i)} \\\vdots \\{x^{({\upsilon - 1})}(i)}\end{bmatrix}}},} & {{Equation}\mspace{14mu} (1)}\end{matrix}$

where the precoding matrix W(i) is of size P×υ with υ as the number oflayers and/or the number of streams for transmission of the PDSCH andi=0, 1, . . . , M_(symb) ^(layer)−1 with M_(symb) ^(layer) as the numberof modulation symbols to transmit per layer for a physical channel.

For p={5, 6, . . . , υ+6}, the WTRU may assume that the base stationcyclically assigns different precoders to different vectors [x⁰(i) . . .x^((υ-1))(i)]^(T) on the PDSCH as described herein below. A differentprecoder may be used in every P′N_(sc) ^(RB) vector, where N_(sc) ^(RB)denotes a resource block size in the frequency domain, (expressed as anumber of subcarriers), and P′ is the precoding resource block group(RBG), (expressed as a number of RBs in the frequency domain). In casethe WTRU is not configured with PRB bundling, P′=1.

The precoder may be selected according to W(i)=C_(k), where k is theprecoder index given by

$k = {{\left( {\left\lfloor \frac{i}{P^{\prime}N_{sc}^{RB}} \right\rfloor {mod}\mspace{14mu} N_{C}} \right) + 1} \in \left\{ {1,2,\ldots \mspace{14mu},N_{C}} \right\}}$

and N_(C) denotes the maximum number of precoders within the codebookcontaining the set of precoders for a given number of layers. Othermethods to select the precoder from the codebook may also beimplemented.

In another example method, a combination of random precoding, cyclicdelay diversity (CDD) and discrete Fourier Transform (DFT) spreading maybe used. In particular, the DM-RS′ and data that are to be transmittedto a WTRU may be first precoded using a randomly selected precoder. Theprecoding granularity may be either per RB or per RBG and each precodermay belong to a codebook which contains a set of precoders known to boththe base station and the WTRU. A large delay CDD followed by DFTspreading may be applied at the subcarrier level on the PDSCH. Thecomposite effect of large delay CDD and DFT spreading may providesignal-to-interference and noise ratio (SINR) averaging across layersfor a given channel realization. Each codeword may be transmitted acrossantennas.

The use of random precoding may cause a different SINR realization overeach layer. FIG. 3 shows the example random precoding. In this examplemethod, both DM-RS and data are subject to the same precoding operation.Therefore, by performing channel estimation using DM-RS, the WTRU mayestimate the effective channel for reception of the PDSCH data.

For large-delay CDD, precoding for SM is defined by:

$\begin{matrix}{{\begin{bmatrix}{y^{(0)}(i)} \\\vdots \\{y^{({P - 1})}(i)}\end{bmatrix} = {{W(i)}{D(i)}{U\begin{bmatrix}{x^{(0)}(i)} \\\vdots \\{x^{({\upsilon - 1})}(i)}\end{bmatrix}}}},} & {{Equation}\mspace{14mu} (2)}\end{matrix}$

where the precoding matrix W(i) is of size P×υ and i=0, 1, . . . ,M_(symb) ^(layer)−1. The matrix U is a fixed DFT precoder, and thematrix D(i) is a diagonal matrix representing the large delay CDDfunctionality. The diagonal size-υ×υ matrix D(i) supporting cyclic delaydiversity and the size-υ×υ matrix U may be given by Table 1 for vε{2, 3,4} layers. For vε{5, 6, 7, 8}, the matrix U and diagonal matrix D(i) maybe given by Tables 2 and 3, respectively. As described herein above, thematrix W is the precoder defined for CL-SM. For p={5, 6, . . . , υ+6},the WTRU may assume that the base station cyclically assigns differentprecoders to different vectors [x⁽⁰⁾(i) . . . x^((υ-1))(i)]^(T) on thePDSCH wherein a different precoder is used every 71 vectors.

TABLE 1 Number of layers υ U D(i) 2 $\frac{1}{\sqrt{2}}\begin{bmatrix}1 & 1 \\1 & ^{{- {j2\pi}}/2}\end{bmatrix}$ $\quad\begin{bmatrix}1 & 0 \\0 & ^{{- {j2\pi}}\; {i/2}}\end{bmatrix}$ 3 $\frac{1}{\sqrt{3}}\begin{bmatrix}1 & 1 & 1 \\1 & ^{{- {j2\pi}}/3} & ^{{- {j4\pi}}/3} \\1 & ^{{- {j4\pi}}/3} & ^{{- {j8\pi}}/3}\end{bmatrix}$ $\quad\begin{bmatrix}1 & 0 & 0 \\0 & ^{{- {j2\pi}}\; {i/3}} & 0 \\0 & 0 & ^{{- {j4\pi}}\; {i/3}}\end{bmatrix}$ 4 $\frac{1}{2}\begin{bmatrix}1 & 1 & 1 & 1 \\1 & ^{{- {j2\pi}}/4} & ^{{- {j4\pi}}/4} & ^{{- {j6\pi}}/4} \\1 & ^{{- {j4\pi}}/4} & ^{{- {j8\pi}}/4} & ^{{- {j12\pi}}/4} \\1 & ^{{- {j6\pi}}/4} & ^{{- {j12\pi}}/4} & ^{{- {j18\pi}}/4}\end{bmatrix}$ $\quad\begin{bmatrix}1 & 0 & 0 & 0 \\0 & ^{{- {j2\pi}}\; {i/4}} & 0 & 0 \\0 & 0 & ^{{- {j4\pi}}\; {i/4}} & 0 \\0 & 0 & 0 & ^{{- {j6\pi}}\; {i/4}}\end{bmatrix}$

TABLE 2 Number of layers υ U 5 $\frac{1}{\sqrt{5}}\begin{bmatrix}1 & 1 & 1 & 1 & 1 \\1 & ^{{- {j2\pi}}/5} & ^{{- {j4\pi}}/5} & ^{{- {j6\pi}}/5} & ^{{- {j8\pi}}/5} \\1 & ^{{- {j4\pi}}/5} & ^{{- {j8\pi}}/5} & ^{{- {j12\pi}}/5} & ^{{- {j16\pi}}/5} \\1 & ^{{- {j6\pi}}/5} & ^{{- {j12\pi}}/5} & ^{{- {j18\pi}}/5} & ^{{- {j24\pi}}/5} \\1 & ^{{- {j8\pi}}/5} & ^{{- {j16\pi}}/5} & ^{{- {j24\pi}}/5} & ^{{- {j32\pi}}/5}\end{bmatrix}$ 6 $\frac{1}{\sqrt{6}}\begin{bmatrix}1 & 1 & 1 & 1 & 1 & 1 \\1 & ^{{- {j2\pi}}/6} & ^{{- {j4\pi}}/6} & ^{{- {j6\pi}}/6} & ^{{- {j8\pi}}/6} & ^{{- {j10\pi}}/6} \\1 & ^{{- {j4\pi}}/6} & ^{{- {j8\pi}}/6} & ^{{- {j12\pi}}/6} & ^{{- {j16\pi}}/6} & ^{{- {j20\pi}}/6} \\1 & ^{{- {j6\pi}}/6} & ^{{- {j12\pi}}/6} & ^{{- {j18\pi}}/6} & ^{{- {j24\pi}}/6} & ^{{- {j30\pi}}/6} \\1 & ^{{- {j8\pi}}/6} & ^{{- {j16\pi}}/6} & ^{{- {j24\pi}}/6} & ^{{- {j32\pi}}/6} & ^{{- {j40\pi}}/6} \\1 & ^{{- {j10\pi}}/6} & ^{{- {j20\pi}}/6} & ^{{- {j30\pi}}/6} & ^{{- {j40\pi}}/6} & ^{{- {j50\pi}}/6}\end{bmatrix}$ 7 $\frac{1}{\sqrt{7}}\begin{bmatrix}1 & 1 & 1 & 1 & 1 & 1 & 1 \\1 & ^{{- {j2\pi}}/7} & ^{{- {j4\pi}}/7} & ^{{- {j6\pi}}/7} & ^{{- {j8\pi}}/7} & ^{{- {j10\pi}}/7} & ^{{- {j12\pi}}/7} \\1 & ^{{- {j4\pi}}/7} & ^{{- {j8\pi}}/7} & ^{{- {j12\pi}}/7} & ^{{- {j16\pi}}/7} & ^{{- {j20\pi}}/7} & ^{{- {j24\pi}}/7} \\1 & ^{{- {j6\pi}}/7} & ^{{- {j12\pi}}/7} & ^{{- {j18\pi}}/7} & ^{{- {j24\pi}}/7} & ^{{- {j30\pi}}/7} & ^{{- {j36\pi}}/7} \\1 & ^{{- {j8\pi}}/7} & ^{{- {j16\pi}}/7} & ^{{- {j24\pi}}/7} & ^{{- {j32\pi}}/7} & ^{{- {j40\pi}}/7} & ^{{- {j48\pi}}/7} \\1 & ^{{- {j10\pi}}/7} & ^{{- {j20\pi}}/7} & ^{{- {j30\pi}}/7} & ^{{- {j40\pi}}/7} & ^{{- {j50\pi}}/7} & ^{{- {j60\pi}}/7} \\1 & ^{{- {j12\pi}}/7} & ^{{- {j24\pi}}/7} & ^{{- {j36\pi}}/7} & ^{{- {j48\pi}}/7} & ^{{- {j60\pi}}/7} & ^{{- {j72\pi}}/7}\end{bmatrix}$ 8 $\frac{1}{2\sqrt{2}}\begin{bmatrix}1 & 1 & 1 & 1 & 1 & 1 & 1 & 1 \\1 & ^{{- {j2\pi}}/8} & ^{{- {j4\pi}}/8} & ^{{- {j6\pi}}/8} & ^{{- {j8\pi}}/8} & ^{{- {j10\pi}}/8} & ^{{- {j12\pi}}/8} & ^{{- {j14\pi}}/8} \\1 & ^{{- {j4\pi}}/8} & ^{{- {j8\pi}}/8} & ^{{- {j12\pi}}/8} & ^{{- {j16\pi}}/8} & ^{{- {j20\pi}}/8} & ^{{- {j24\pi}}/8} & ^{{- {j28\pi}}/8} \\1 & ^{{- {j6\pi}}/8} & ^{{- {j12\pi}}/8} & ^{{- {j18\pi}}/8} & ^{{- {j24\pi}}/8} & ^{{- {j30\pi}}/8} & ^{{- {j36\pi}}/8} & ^{{- {j42\pi}}/8} \\1 & ^{{- {j8\pi}}/8} & ^{{- {j16\pi}}/8} & ^{{- {j24\pi}}/8} & ^{{- {j32\pi}}/8} & ^{{- {j40\pi}}/8} & ^{{- {j48\pi}}/8} & ^{{- {j56\pi}}/8} \\1 & ^{{- {j10\pi}}/8} & ^{{- {j20\pi}}/8} & ^{{- {j30\pi}}/8} & ^{{- {j40\pi}}/8} & ^{{- {j50\pi}}/8} & ^{{- {j60\pi}}/8} & ^{{- {j70\pi}}/8} \\1 & ^{{- {j12\pi}}/8} & ^{{- {j24\pi}}/8} & ^{{- {j36\pi}}/8} & ^{{- {j48\pi}}/8} & ^{{- {j60\pi}}/8} & ^{{- {j72\pi}}/8} & ^{{- {j84\pi}}/8} \\1 & ^{{- {j14\pi}}/8} & ^{{- {j28\pi}}/8} & ^{{- {j42\pi}}/8} & ^{{- {j56\pi}}/8} & ^{{- {j70\pi}}/8} & ^{{- {j84\pi}}/8} & ^{{- {j98\pi}}/8}\end{bmatrix}$

TABLE 3 Number of layers υ D(i) 5 $\quad\begin{bmatrix}1 & 0 & 0 & 0 & 0 \\0 & ^{{- {j2\pi}}\; {i/5}} & 0 & 0 & 0 \\0 & 0 & ^{{- {j4\pi}}\; {i/5}} & 0 & 0 \\0 & 0 & 0 & ^{{- {j6\pi}}\; {i/5}} & 0 \\0 & 0 & 0 & 0 & ^{{- {j8\pi}}\; {i/5}}\end{bmatrix}$ 6 $\quad\begin{bmatrix}1 & 0 & 0 & 0 & 0 & 0 \\0 & ^{{- {j2\pi}}\; {i/6}} & 0 & 0 & 0 & 0 \\0 & 0 & ^{{- {j4\pi}}\; {i/6}} & 0 & 0 & 0 \\0 & 0 & 0 & ^{{- {j6\pi}}\; {i/6}} & 0 & 0 \\0 & 0 & 0 & 0 & ^{{- {j8\pi}}\; {i/6}} & 0 \\0 & 0 & 0 & 0 & 0 & ^{{- {j10\pi}}\; {i/6}}\end{bmatrix}$ 7 $\quad{\quad\begin{bmatrix}1 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & ^{{- {j2\pi}}\; {i/7}} & 0 & 0 & 0 & 0 & 0 \\0 & 0 & ^{{- {j4\pi}}\; {i/7}} & 0 & 0 & 0 & 0 \\0 & 0 & 0 & ^{{- {j6\pi}}\; {i/7}} & 0 & 0 & 0 \\0 & 0 & 0 & 0 & ^{{- {j8\pi}}\; {i/7}} & 0 & 0 \\0 & 0 & 0 & 0 & 0 & ^{{- {j10\pi}}\; {i/7}} & 0 \\0 & 0 & 0 & 0 & 0 & 0 & ^{{- {j12\pi}}\; {i/7}}\end{bmatrix}}$ 8 $\quad{\quad\begin{bmatrix}1 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\0 & ^{{- {j2\pi}}\; {i/8}} & 0 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & ^{{- {j4\pi}}\; {i/8}} & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & ^{{- {j6\pi}}\; {i/8}} & 0 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & ^{{- {j8\pi}}\; {i/8}} & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & ^{{- {j10\pi}}\; {i/8}} & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 0 & ^{{- {j12\pi}}\; {i/8}} & 0 \\0 & 0 & 0 & 0 & 0 & 0 & 0 & ^{{- {j14\pi}}\; {i/8}}\end{bmatrix}}$

In the event that the CDD may be applied to both the DM-RS and PDSCH,the large delay CDD would be equivalent to layer shifting. For example,in a four-layer transmission, on the first subcarrier of a given RB,layers 1, 2, 3, 4 (in this order) are transmitted over 4 spatialchannels; on the second subcarrier, layer 4, 1, 2, 3 (in this order) aretransmitted over 4 spatial channels, and so on. Since the DM-RS existson the 1^(st), 2^(nd), 6^(th), 7^(th), 11^(th) and 12^(th) subcarriers,if the DM-RS is precoded in the same way as physical uplink sharedchannel (PUSCH) data, the channel estimation may be obtained as shown inTable 4.

TABLE 4 Subcarrier used for 1st 2nd 6th 7th 11th 12th channel estimationSpatial channel to 1^(st) and 2^(nd) and 4^(th) and 1^(st) and 3^(rd)and 4^(th) and be estimated 2^(nd) 3^(rd) 1^(st) 2^(nd) 4^(th) 1^(st)

As shown in Table 4, the DM-RS density becomes non-uniform acrossspatial channels, which may cause performance degradation. To improveDM-RS channel estimation, the channel estimation may be performed asshown in Table 5.

TABLE 5 Subcarrier used for 1st 2nd 6th 7th 11th 12th channel estimationSpatial channel to 1^(st) and 3^(rd) and 1^(st) and 3^(rd) and 1^(st)and 3^(rd) and be estimated 2^(nd) 4^(th) 2^(nd) 4^(th) 2^(nd) 4^(th)

As shown in Table 5, DM-RS becomes uniformly distributed. This DM-RSdesign may allow averaging or filtering between multiple symbols tofurther improve DM-RS channel estimation. In other words, in order toachieve the desired DM-RS property, the DM-RS may be precodeddifferently than data. For example, the large delay CDD matrix D(i) maybe dropped in the DM-RS precoding. Alternatively, the DM-RS may bepre-shifted before precoding is performed if D(i) is desired.

In another example method, the data and DM-RS may be precodedseparately. In this method, the DM-RS′ and data to be transmitted to aWTRU may each be precoded using a different randomly selected precoder.The precoding granularity of PDSCH may be different from that of theDM-RS. The precoding granularity for the DM-RS may be either per RB orper RBG, while the precoding granularity for the PDSCH may be at thesubcarrier-level, RB-level or RBG-level. Each precoder may belong to adifferent codebook, each containing a set of precoders. In this method,given that the DM-RS and data are subject to different precodingoperations, the WTRU may assume that the transmit precoding informationfor both the DM-RS and PDSCH are known to both the base station and theWTRU.

In another example method, the precoding on the DM-RS may be completelybypassed, (i.e., no precoding is performed on DM-RS). Alternatively, theprecoding on the DM-RS may be fixed or semi-static, (e.g., the WTRU mayreceive the DM-RS precoding information via radio resource control (RRC)signaling or the DM-RS precoding may be fixed in the specifications).

Given that the precoder applied to the DM-RS is different from that ofthe PDSCH, regardless of whether or not the DM-RS is precoded, the WTRUmay not assume that the estimated channel using the DM-RS is theeffective channel for the PDSCH detection. In other words, the WTRU mayperform a channel estimation using the DM-RS for up to eight physicaltransmit antennas regardless of the number of layers, (assuming that thetransmit precoding information is available). Accordingly, the WTRU mayneed to be informed regarding the number of physical transmit antennasin addition to the number of layers. The WTRU may obtain thisinformation using one of the example methods described herein below.

In an example method, the WTRU may be semi-statically configured viahigher layer signaling or informed through downlink allocation, (i.e.,via a PDCCH), regarding the number of layers and the number of physicalantennas at the base station.

In another example method, the WTRU may assume that the number of DM-RSantenna ports is the same as the number of channel state informationreference signal (CSI-RS) antenna ports. In the event that multipleCSI-RS configurations are used in a given cell, the WTRU may assume oneCSI-RS configuration may be associated with the number of DM-RS antennaports. The WTRU may assume that the CSI-RS configuration with a non-zerotransmission power is the reference configuration for implicitderivation of the number of DM-RS antenna ports. Alternatively, the WTRUmay assume that one of the CSI-RS configurations with a zerotransmission power may be the reference configuration for implicitderivation of the number of DM-RS antenna ports.

Alternatively, the WTRU may derive the number of DM-RS antenna portsblindly. Given that there is a 3 dB power boosting on the DM-RS whenboth code-division multiplexed groups are used for the DM-RS, the WTRUmay blindly detect the number of DM-RS antenna ports through powerdetection.

In addition to random precoding, the large delay CDD together with DFTspreading may be applied at the subcarrier-level on the PDSCH. The WTRUmay assume that information regarding the large delay CDD matrix, theDFT spreading matrix and the precoder are available for PDSCH detection.

The WTRU may use the channel estimates obtained from the DM-RS andderive the effective channel using the known precoding on the DM-RS. TheWTRU may then detect the PDSCH based on the knowledge of the CDD, DFT,and precoder matrices used for data.

Described herein are example methods used for heterogeneous deploymentsand may be applicable to other deployments as well. Hereafter, thetransmission point for geographically distributed antennas refers to aremote radio head (RRH), a relay, or a macro cell.

In order to achieve spatial diversity gain in the case of geographicallydistributed antennas at the transmitting side, the WTRU may receive eachRB within its downlink allocation from different transmission points.This technique is particularly beneficial in cases where the signalstransmitted from one or multiple transmission points are experiencingsever shadowing. The spatial diversity gain is achieved through the useof a channel encoder, which is applied on multiple RBs within atransport block.

Dynamic resource scheduling may be used to achieve spatial diversitygain. In this method, the scheduler performs dynamic resourcepartitioning between different transmission points in all domainsincluding time, frequency, or space. Scheduling is performed based onthe WTRU's channel quality feedback. More specifically, the base stationmay assign each transmission point a separate CSI-RS resource. The WTRUmay then be configured via higher layer signaling with one or multipleCSI-RS configurations to perform channel measurement and provide channelquality feedback for each transmission point. In order to facilitatefrequency domain scheduling, the channel quality reports may beper-subband, where a subband is a collection of sub-carriers that havebeen allocated for scheduling of data. In this case, unlike the legacysystems where the CSI-RS configuration is cell-specific, the CSI-RSconfiguration may be WTRU-specific. The WTRU may expect theconfiguration of CSI-RS and/or zero-power CSI-RS and physical multicastchannel (PMCH) in the same subframe of a serving cell.

Transmission point hopping may be used to achieve spatial diversitygain. In this method, the scheduler may apply a hopping scheme acrosstransmission points while performing dynamic resource partitioning intemporal and/or frequency domains. For a given subframe, the WTRU mayreceive each RB from a different or randomly selected transmissionpoint. The transmission point may belong to a set of transmission pointsthat are allocated by the scheduler to serve the WTRU. Given that eachresource allocation comprises multiple RBs, by sweeping across differenttransmission points, the spatial diversity gain is maximized through thechannel decoding process. The chance of experiencing severe shadowing bythe WTRU is substantially reduced by randomly choosing a transmissionpoint.

Described herein are transmission point pairing or sets. Transmissionpoints that exhibit similar but uncorrelated channel conditions may bepaired or defined in a set by the base station, for either dynamicresource scheduling or transmission point hopping. For example,transmission points in an indoor environment may be defined as belongingto the same set.

A transmission point set may be defined for transmission points whichhave a similar number of antennas, or similar rank capability.Alternatively, a transmission point set may be associated with aparticular WTRU category, or categories, that it supports.Alternatively, a transmission point set may be associated with aparticular CSI-RS measurement set. The OL-SM used at each transmissionpoint may be as described herein above or a conventional OL-SM asspecified in, for example, LTE R8.

Described herein is an example method for precoding data and DM-RSjointly for at least heterogeneous deployments. A randomly selectedprecoder may be applied at each RB or RBG transmitted from a differenttransmission point. FIG. 4 shows an example OL-SM system 400 forgeographically distributed transmit antennas. OL-SM system 400 mayinclude a base station 405 defining a macro cell 405, a RRH 410, a RRH415. a RRH 420, a WTRU 425 and a WTRU 430. When referring to randomprecoder selection, it should be understood that the sequence ofprecoder selection may be pre-defined and/or cyclical.

In one example method, the base station may define a set of cyclicallydefined precoders. The set of cyclically defined precoders may becyclically rotated through a number of transmission points which use thesame cell ID in a cell or may be defined for a transmission point set.In another example, the methods described herein may be applied totransmission points at the edge of the cell, to transmission pointswhich exhibit a greater degree of interference from adjacenttransmission points and/or to cells which use a different cell ID.

The precoded P_(l)×1 vector at the lth transmission point for OL-SM,(where P_(l) is the number of transmit antennas at the lth transmissionpoint), may be defined as follows:

$\begin{matrix}{{\begin{bmatrix}{y_{l}^{(0)}(i)} \\\vdots \\{y_{l}^{P_{l} - 1}(i)}\end{bmatrix} = {{W_{l}(i)}\begin{bmatrix}{x^{(0)}(i)} \\\vdots \\{x^{({\upsilon - 1})}(i)}\end{bmatrix}}},} & {{Equation}\mspace{14mu} (3)}\end{matrix}$

where the precoding matrix W_(l)(i) is of size P_(l)×υ with υ as thenumber of layers for transmission of the PDSCH, i=0, 1, . . . , M_(symb)^(layer)−1 with M_(symb) ^(layer) as the number of modulation symbols totransmit per layer for a physical channel and l=0, 1, . . . , L−1 with Las the number of transmission points serving the WTRU. For p={7, 8, . .. υ+6}, the WTRU may assume that the base station cyclically assignsdifferent precoders and different transmission points to differentvectors [x⁽⁰⁾(i) . . . x^((υ-1))(i)]^(T) on the PDSCH.

The precoders used at each transmission point may belong to the samecodebook or a different codebook, depending on the number of physicalantennas and/or number of layers supported at each transmission point.The WTRU may not assume that the precoder applied at each RB within themultiple allocated RBs belongs to the same codebook. For example, assumethat the set of transmission points which serves the WTRU 425 includesthe base station 405 and two RRHs 410 and 415 and that the WTRU 425 isequipped with two antennas while the base station 405 and the two RRHs410 and 415 are equipped with eight and four antennas, respectively. Fortransmission on two layers, (i.e., rank=2), the size of the precodermatrices used at the base station 405 is 8 by 2 while the size of thoseused at the RRHs 410 and 415 is 4 by 2.

Described herein is a combination of random precoding, CDD and DFTspreading used for at least heterogeneous deployments. In addition torandom precoding, a combination of large delay CDD and/or DFT spreadingmay be applied to benefit from the increased frequency selectivity. Forlarge delay CDD with DFT spreading, precoding for spatial multiplexingusing geographically distributed antennas may be defined as follows:

$\begin{matrix}{{\begin{bmatrix}{y_{l}^{(0)}(i)} \\\vdots \\{y_{l}^{P_{l} - 1}(i)}\end{bmatrix} = {{W_{l}(i)}{D(i)}{U\begin{bmatrix}{x^{(0)}(i)} \\\vdots \\{x^{({\upsilon - 1})}(i)}\end{bmatrix}}}},} & {{Equation}\mspace{14mu} (4)}\end{matrix}$

where the precoding matrix W (i) is of size P_(l)×υ and i=0, 1, . . . ,M_(symb) ^(layer)−1. The diagonal size-υ×υ matrix D(i) supporting cyclicdelay diversity and the size-υ×υ matrix U are both given in Table 1 forvε{2, 3, 4} layers and for vε{5, 6, 7, 8}, the matrix U and diagonalmatrix D(i) may be given by Table 2 and Table 3, respectively.

Described herein are methods to achieve spatial multiplexing usingmultiple transmission points. Different layers for OL-SM may betransmitted from different transmission points. This is particularlybeneficial in cases where the signals transmitted from one transmissionpoint are spatially correlated. The high spatial correlation results insignificant reduction of MIMO channel capacity and may occur whenantenna spacing is insufficient or there is a lack of rich scatteringenvironment.

By splitting the layers across the uncorrelated geographicallydistributed antennas, the OL-SM may be used for high rank transmissions.In other words, the number of layers for spatial multiplexing maypotentially exceed the four layers specified for OL-SM in LTE Rel-8.

The application of a fixed DFT-based precoding may ensure that thechannel coefficients of the antenna ports are uncorrelated. In oneexample method, the fixed DFT precoder may be removed from thetransmission chain. For large delay CDD, precoding for spatialmultiplexing using geographically distributed antennas may be defined asfollows:

$\begin{matrix}{{\begin{bmatrix}{y^{(0)}(i)} \\\vdots \\{y^{({P - 1})}(i)}\end{bmatrix} = {{W(i)}{{D(i)}\begin{bmatrix}{x^{(0)}(i)} \\\vdots \\{x^{({\upsilon - 1})}(i)}\end{bmatrix}}}},} & {{Equation}\mspace{14mu} (5)}\end{matrix}$

where the precoding matrix W(i) is of size P×υ and i=0, 1, . . . ,M_(symb) ^(layer)−1. The diagonal size-υ×υ matrix D(i) supporting cyclicdelay diversity is given by Table 1 for vε{2, 3, 4} and Tables 2 and 3for vε{5, 6, 7, 8}, respectively.

Described herein are example channel quality indicator (CQI)/rankindicator (RI) reporting methods. Given that LTE R10 WTRUs and beyondmay support DM-RS as part of transmission modes 8 and 9, the WTRU may beconfigured with transmission mode 8 or 9 or one of their descendents forOL-SM.

A number of channel quality indicator (CQI) or rank indicator (RI)reporting methods may be defined to support OL-SM. For aperiodic CSIfeedback on PUSCH, reporting modes 2-0 and 3-0 from LTE R8 or R10 may beextended to transmission modes 8 and 9 or one of their descendents tosupport OL-SM, where reporting mode 2-0 refers to WTRU-selected subbandfeedback and reporting mode 3-0 refers to higher layer-configuredsubband feedback.

For transmission modes 8 and 9 in LTE R10, the reporting modes 2-0 and3-0 are supported when the WTRU is configured without precoding matrixindicator (PMI)/RI reporting or when the number of CSI-RS ports is equalto one. However, to support OL-SM, there is a need for the WTRU tofeedback both CQI and rank. The WTRU may be configured with multipleCSI-RS ports for channel measurements in order to support a rank higherthan one. The WTRU may report an RI as a part of reporting modes 2-0 and3-0. The restriction on the number of CSI-RS ports to be used by theWTRU for channel measurements under reporting modes 2-0 and 3-0 may beremoved. In other words, for transmission modes 8 and 9, certainreporting modes may be supported on the PUSCH. For transmission mode 8,modes 1-2, 2-2, and 3-1 if the WTRU is configured with PMI/RI reportingand modes 2-0 and 3-0 if the WTRU is configured without PMI reporting.For transmission mode 9, modes 1-2, 2-2, and 3-1 if the WTRU isconfigured with PMI/RI reporting and number of CSI-RS ports >1 and modes2-0 and 3-0 if the WTRU is configured without PMI reporting and numberof CSI-RS ports ≧1.

With respect to the WTRU procedures for reporting modes 2-0 and 3-0, fortransmission modes 8 and 9, the WTRU may calculate the reported CQIvalues conditioned on the reported RI.

As for periodic CSI reporting using a physical uplink control channel(PUCCH), reporting modes 1-0 and 2-0 from LTE R8/10 may be extended totransmission modes 8 and 9 or one of their descendents to support OL-SM.In the context of LTE R8, reporting mode 1-0 represents widebandfeedback and reporting mode 2-0 refers to WTRU-selected subbandfeedback.

Similar to aperiodic CSI reporting using PUSCH, there are currently somerestrictions on the use of reporting modes 1-0 and 2-0 by the WTRU undertransmission modes 8 and 9. To enable RI reporting and configuration ofmore than one CSI-RS port, the WTRU may support the following periodicCSI reporting. For transmission mode 8, modes 1-1 and 2-1 if the WTRU isconfigured with PMI/RI reporting and modes 1-0 and 2-0 if the WTRU isconfigured without PMI reporting. For transmission mode 9, modes 1-1 and2-1 if the WTRU is configured with PMI/RI reporting and the number ofCSI-RS ports >1 and modes 1-0 and 2-0 if the WTRU is configured withoutPMI reporting or the number of CSI-RS ports ≧1.

With respect to the WTRU procedures for reporting modes 1-0 and 2-0, fortransmission modes 8 and 9, the WTRU may calculate the CQI valuesconditioned on the last reported periodic RI.

In the above example, the rank report may be associated to a particulartransmission point as a result of scheduling by the base station, or itmay be associated with the combined rank of one or more transmissionpoints. In the later case, the CQI reference sub-band for reporting CQImay assume the minimum of the rank of the associated transmissionpoints. For more than two transmission points, this may by inference,imply the CQI report is for at least a 2 or greater rank.

The WTRU may transmit the CQI/RI reports using time divisionmultiplexing (TDM) for transmission points defined in the above examplesin a cyclic manner. In order to reduce the feedback overhead, a singlerank report (RI) may be sent for one or multiple transmission points ina particular reporting instance.

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element can be used alone or in any combination with theother features and elements. In addition, the methods described hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable medium for execution by a computeror processor. Examples of computer-readable media include electronicsignals (transmitted over wired or wireless connections) andcomputer-readable storage media. Examples of computer-readable storagemedia include, but are not limited to, a read only memory (ROM), arandom access memory (RAM), a register, cache memory, semiconductormemory devices, magnetic media such as internal hard disks and removabledisks, magneto-optical media, and optical media such as CD-ROM disks,and digital versatile disks (DVDs). A processor in association withsoftware may be used to implement a radio frequency transceiver for usein a WTRU, UE, terminal, base station, RNC, or any host computer.

1. A method implemented at a first apparatus having transmit and receivechains and a plurality of antennas configured for multiple-inputmultiple-output (MIMO) communication, the method comprising: randomlyselecting at least one precoder; precoding data and dedicated referencesignals specific to the first apparatus using the at least one precoderto generate precoded data and precoded dedicated reference signals; andtransmitting the precoded data and the precoded dedicated referencesignals via the plurality of antennas to a plurality of apparatuses,each having transmit and receive chains and one or more antennasconfigured for MIMO communication.
 2. The method of claim 1, wherein thededicated reference signals are demodulation reference signals.
 3. Themethod of claim 1, wherein precoding data and dedicated referencesignals comprises precoding the dedicated reference signals differentlythan the data.
 4. The method of claim 1, wherein the at least oneprecoder is one of a predefined precoder selection sequence.
 5. Themethod of claim 1, further comprising: selecting a first precoder forprecoding a first number of resource blocks (RBs); and selecting asecond precoder, different from the first precoder, for precoding asecond number of RBs.
 6. The method of claim 1, wherein a precodinggranularity for the dedicated reference signals is different than aprecoding granularity for the data.
 7. A method implemented at a firstapparatus having transmit and receive chains and a plurality of antennasconfigured for multiple-input multiple-output (MIMO) communication, themethod comprising: randomly selecting at least one precoder; precodingdata and dedicated reference signals specific to the first apparatususing the at least one precoder to generate precoded data and precodeddedicated reference signals, wherein the data is precoded differentlythan the dedicated reference signals; and transmitting the precoded dataand the precoded dedicated reference signals via the plurality ofantennas to at least one second apparatus having transmit and receivechains and one or more antennas configured for MIMO communication. 8.The method of claim 7, wherein the dedicated reference signals aredemodulation reference signals.
 9. The method of claim 7, wherein the atleast one precoder is one of a predefined precoder selection sequence.10. The method of claim 7, wherein a precoding granularity for thededicated reference signals is different than a precoding granularityfor the data.
 11. An apparatus comprising transmit and receive chainsand a plurality of antennas configured for multiple-inputmultiple-output (MIMO) communication, wherein: the transmit chain isconfigured to: randomly select at least one precoder; precode data anddedicated reference signals specific to the first apparatus using the atleast one precoder to generate precoded data and precoded dedicatedreference signals; and transmit the precoded data and the precodeddedicated reference signals via the plurality of antennas to a pluralityof other apparatuses, each having transmit and receive chains and one ormore antennas configured for MIMO communication.
 12. The apparatus ofclaim 11, wherein the dedicated reference signals are demodulationreference signals.
 13. The apparatus of claim 11, wherein the transmitchain is configured to precode the dedicated reference signalsdifferently than the data.
 14. The apparatus of claim 11, wherein the atleast one precoder is one of a predefined precoder selection sequence.15. The apparatus of claim 11, wherein the transmit chain is furtherconfigured to: selecting a first precoder for precoding a first numberof resource blocks (RBs); and selecting a second precoder, differentfrom the first precoder, for precoding a second number of RBs.
 16. Theapparatus of claim 11, wherein a precoding granularity for the dedicatedreference signals is different than a precoding granularity for thedata.
 17. An apparatus comprising transmit and receive chains and aplurality of antennas configured for multiple-input multiple-output(MIMO) communication, wherein: the transmit chain is configured to:randomly select at least one precoder; precode data and dedicatedreference signals specific to the first apparatus using the at least oneprecoder to generate precoded data and precoded dedicated referencesignals, wherein the data is precoded differently than the dedicatedreference signals; and transmit the precoded data and the precodeddedicated reference signals via the plurality of antennas to at leastone second apparatus having transmit and receive chains and one or moreantennas configured for MIMO communication.
 18. The apparatus of claim17, wherein the dedicated reference signals are demodulation referencesignals.
 19. The apparatus of claim 17, wherein the at least oneprecoder is one of a predefined precoder selection sequence.
 20. Theapparatus of claim 17, wherein a precoding granularity for the dedicatedreference signals is different than a precoding granularity for thedata.
 21. A method implemented at a first apparatus having transmit andreceive chains and a plurality of antennas configured for multiple-inputmultiple-output (MIMO) communication, the method comprising: receivingchannel quality feedback for each one of the plurality of transmitantennas; and transmitting data from the plurality of antennas accordingto resources dynamically partitioned among the plurality of antennasbased on a plurality of domains, wherein transmitting the data from theplurality of antennas comprises transmitting different layers of datafrom different antennas.
 22. The method of claim 21, further comprising:assigning each antenna of the plurality of antennas a separate channelstate information (CSI) reference signal (RS) resource.
 23. The methodof claim 21, further comprising: applying a randomly selected precoderfor each resource block (RB) or resource block group (RBG) transmittedfrom a different antenna.
 24. The method of claim 21, wherein theplurality of domains includes time, frequency and space.
 25. Anapparatus comprising transmit and receive chains and a plurality ofantennas configured for multiple-input multiple-output (MIMO)communication, wherein: the receive chain is configured to receivechannel quality feedback for each one of the plurality of transmitantennas; and the transmit chain is configured to transmit differentlayers of data from different antennas of the plurality of antennasaccording to resources dynamically partitioned among the plurality ofantennas based on a plurality of domains.
 26. The apparatus of claim 25,wherein each antenna of the plurality of antennas is assigned a separatechannel state information (CSI) reference signal (RS) resource.
 27. Theapparatus of claim 25, wherein the transmit chain is further configuredto: apply a randomly selected precoder for each resource block (RB) orresource block group (RBG) transmitted from a different antenna.
 28. Theapparatus of claim 25, wherein the plurality of domains includes time,frequency and space.